Frank,

Sorry for the confusion.  I thought that turning off cache using hdparm -W
0 /dev/sdx takes effect right away and in case of non-raid controllers and
Seagate or Micron SSDs I would see a difference starting fio benchmark
right after executing hdparm.  So I wonder it makes a difference whether
cache turned off before OSD started or after.



On Tue, Jan 21, 2020, 2:07 AM Frank Schilder <fr...@dtu.dk> wrote:

> > So hdparam -W 0 /dev/sdx doesn't work or it makes no difference?
>
> I wrote "We found the raw throughput in fio benchmarks to be very
> different for write-cache enabled and disabled, exactly as explained in the
> performance article.", so yes, it makes a huge difference.
>
> > Also I am not sure I understand why it should happen before OSD have
> been started.
> > At least in my experience hdparam does it to hardware regardless.
>
> I'm not sure I understand this question. Ideally it happens at boot time
> and if this doesn't work, at least sometimes before the OSD is started. Why
> and how else would one want this to happen?
>
> Best regards,
>
> =================
> Frank Schilder
> AIT Risø Campus
> Bygning 109, rum S14
>
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